In the past, different communications networks like public land mobile networks (PLMN), public switched telephone networks (PSTN) and data/IP networks (e.g. the public Internet) have co-existed in the form of separate monolithic networks vertically aligned with respect to each other. In each of these monolithic networks, network control and connectivity, i.e., the transfer of user data, have traditionally been bundled.
Today, mobile communication is migrating toward 3rd generation networks like the universal mobile telecommunication system (UMTS). In parallel with the migration toward 3rd generation mobile networks, a network architecture that is based on horizontal planes replaces the traditional vertical network architectures. According to the horizontal approach of modern network architectures, the tasks of network control and connectivity are being split into different horizontal planes, namely a network control plane and a connectivity plane.
The connectivity plane is based primarily on cell- and packet-based data transfer technologies like the asynchronous transfer mode (ATM) and the Internet protocol (IP). An important task of the connectivity plane is to provide interfaces to present-day telecommunications networks—which are based on time-division multiplexing (TDM)—and to legacy networks, such as PSTN. Due to this interfacing task of the connectivity plane, network nodes are required that bridge between different transmission technologies and that add additional services (like bandwidth on demand) to end-user connections. Media gateways (MGW) as described in Magnus Fyrö et al, “Media gateway for mobile networks”, Ericsson Review no. 4, 2000, 216 to 223, are a possible realization of such bridging nodes.
In context with the transmission toward horizontally oriented network architectures, conventional TDM network nodes like mobile services switching centers (MSCs), which traditionally include network control tasks and connectivity tasks in the same node, are separated into a MGW and a dedicated server component (MSC server). In conventional general packet radio service (GPRS) networks a similar migration takes place. The conventional serving GPRS support node (SGSN) is split into a MGW and a dedicated server component (SGSN server). Whereas in the network control plane the MSC server controls circuit-mode services and the SGSN server controls packet-mode services, a MGW in the connectivity plane may be common to both circuit-mode and packet-mode networks.
This situation is depicted in the exemplary network architecture depicted in FIG. 1. The upper half FIG. 1 corresponds to the network control plane including components like the MSC server or the SGSN server, whereas the lower half corresponds to the connectivity plane including components like MGWs. In FIG. 1, fine lines represent control connections captioned with the respective control protocol, and thicker lines represent data transfer connections.
In the exemplary scenario of FIG. 1, a call between an UMTS terrestrial radio access network (UTRAN) or a basestation subsystem (BSS) and a PSTN is interconnected by two different MGWs. MGW A interfaces the UTRAN and BSS and switches ATM or routes IP traffic. The MSC server and the SGSN server both have a control connection to UTRAN and BSS. MGW B interfaces the PSTN and is controlled using the H.248 control protocol by the MSC server and a gateway MSC (GMSC)/transit switching center (TSC) server.
If in a scenario as depicted in FIG. 1 a call is to be set up to a mobile terminal, different network nodes may be involved. Usually, the network nodes involved are determined by the network type from which the call originates and the network type in which the call terminates. In order to better understand the signalling involved in the set up of a call in the scenario depicted in FIG. 1, call set up within a PLMN, e.g. within a global system for mobile communication (GSM) network, is described first.
As is well known, for a mobile terminating call the number given by a calling party points to a record in a GSM home location register (HLR). Among other data, the HLR includes information relating to the current location of the mobile terminal which is called. More specifically, the HLR record for the called mobile terminal contains information necessary for finding the final destination of the call, i.e. the MSC to which the called mobile terminal is currently attached.
In order to set up a call toward a GSM user, this call is first routed to a GMSC, without any knowledge of the whereabouts of the called mobile terminal. The GMSC accesses the HLR of the called mobile terminal to obtain information about the MSC currently associated with this mobile terminal. The HLR then has to interrogate this MSC to obtain routing information. When being contacted by the HLR, the MSC generates routing information in the form of a roaming number chosen from a pool of free numbers, and links it temporarily to the called mobile terminal. The roaming number is given back via the HLR to the GMSC. Using the roaming number as an address, the GMSC can route the call to the MSC to which the mobile terminal is attached. Since this MSC has linked the roaming number to the called mobile terminal, the MSC can go ahead with the establishment of the call toward the called terminal.
If the call originates and terminates within a particular PLMN, none of the components depicted in FIG. 1 will be involved except for the PLNM. The situation is different if a call originating from e.g. a PSTN terminal terminates at a UMTS user equipment (UE). Although the basic principles of setting up a call are similar to those described above in context with GSM, additional network nodes like MGWs, GGSNs, etc. will get involved. Moreover, it is readily apparent that additional mechanisms with respect to the routing of messages for example on the connectivity plane have to be implemented.
Thus, there is a need for a concept for efficiently routing a connectivity plane messages to a mobile terminal.